The present invention relates generally to the field of wireless electronic communications. In particular, the present invention pertains to a specialized communication technique that supports reliable transmission of compressed video (e.g. MPEG video) over fading Internet communication channels.
With the popularization of the Internet and the trend toward incorporating Internet access in wireless electronic devices, such as cellular phones and personal organizers, there has been an increased demand for efficient and reliable transmission of multimedia applications, including compressed video data, over the Internet. Internet Protocol (IP) is a known communication protocol that provides for the transmission of data over the Internet. IP data is transmitted over the Internet in xe2x80x9cpacketsxe2x80x9d wherein each xe2x80x9cpacketxe2x80x9d consists of a header portion and a payload portion. The header portion conveys addressing information while the payload portion contains information bits that represent a segment of user data, such as MPEG video data. Unlike some other communication protocols, the payload portion of IP packets may be of any length.
The wireless Internet is an error-prone environment having low signal to noise ratios and experiencing bursts of errors and periods of fading. Unlike hard-wired communication channels, the wireless Internet is considered a xe2x80x9cnoisyxe2x80x9d or xe2x80x9cfadingxe2x80x9d communication channel that results in high levels of concentrated data transmission errors. To address these errors, various methods have been used. For example, the MPEG-4 standard, one of the most-recently developed video compression standards, supports a wide range of error resilience features that facilitate decoder recovery and error concealment in the event of a transmission error. However, these passive error control techniques do not actually correct channel errors, and the errors still affect the quality of the received video.
Another approach to addressing data errors that result from fading communication channels is to apply error control coding to the IP packets. These error control codes are combined with the headers and payloads of the IP packets before transmission over the wireless Internet and are used by a receiving device to monitor the integrity of the data received and to correct transmission errors in the data. To assure a low packet loss rate, a very powerful code is used for the header portion of each IP packet, and to minimize the overhead associated with error control codes and achieve adequate throughput, a somewhat weaker code is used for the payload portion of each IP packet.
IP transmission of compressed video poses different problems for quality of service as compared to transmission of voice, data, and imagery. To achieve a superior quality of service for MPEG transmissions, it is necessary to deliver a very small bit error rate (BER), on the order of 10xe2x88x926 to 10xe2x88x928, to the video decoder in the receiving device. This acceptable BER range is more stringent than that which is required for the effective transmission of voice, data, and imagery. If the delivered BER is larger than 10xe2x88x926, the degradation in picture quality can result in picture flashes, jumps, jerkiness, or even the entire picture going blank for a period of time. The necessarily low BER has been an impediment to the effective and efficient transmission of MPEG video over severely noisy or fading Internet communication channels because such channels have very high inherent BERs and exhibit a mixture of independent and burst-error phenomena.
Ordinarily, to improve the performance of a coded communication system, the power of the error control codes is increased, thereby increasing the amount of coding overhead. While the additional overhead reduces the system throughput, the more powerful error control codes are better able to ensure the integrity of the data being transmitted. However, this approach is not sufficient in connection with severely fading wireless Internet communication channels. Even when very powerful error control codes are used, severely fading communication channels still result in receipt of excessive uncorrectable error patterns. In particular, the transmission errors incurred over a severely fading channel typically occur in bursts and tend to be very concentrated. Such errors are unacceptable when transmitting MPEG video because of the very low BER required to be delivered to the video decoder.
Accordingly, prior to this invention, the quality of MPEG video transmitted over fading wireless Internet communication channels was inferior. The present invention provides for a superior quality of service for MPEG video on fading Internet communication channels.
The present invention comprises a system and communication technique for IP transmission of compressed video (MPEG) that provides reliable data transmission over fading wireless Internet communication channels. The invented system includes a transmitting device and a receiving device that communicate with each other over the wireless Internet. The transmitting device includes a video encoder, an encapsulator circuit, a Bose-Chaudhuri-Hocquenghem (BCH) link coding circuit, a Reed-Solomon (RS) link coding circuit, an interleaver circuit, and a modulator. The receiving device includes a video decoder, a decapsulator circuit, a BCH link decoding circuit, an RS link decoding circuit, a de-interleaver circuit, and a demodulator. The transmitting device transmits MPEG video data using IP over the wireless Internet to the receiving device.
Prior to transmitting the MPEG data, the transmitting device applies binary BCH error control codes to the header portion of each IP packet and RS error control codes to the payload portion of each IP packet. Then, a predetermined number of IP packets are interleaved. The header portions of each IP packet in the group are interleaved on a bit-by-bit basis, and the payload portions of each IP packet in the group are interleaved on a byte-by-byte basis. The interleaved IP packets are transmitted over the wireless Internet to the receiving device. The receiving device de-interleaves the IP packets, detects and corrects transmission errors in the data, removes the binary BCH and RS error control codes and provides the error-corrected data to the video decoder to ultimately produce video on a display device. The technique of interleaving the IP packets prior to transmission and de-interleaving the IP packets after receipt essentially xe2x80x9cspreads outxe2x80x9d the transmission errors over many IP packets instead of allowing them to be concentrated in a few IP packets. The BCH and RS codes are more effective at detecting and correcting errors in IP packets if each packet contains a relatively small number of errors.